Enhanced photocatalytic degradation of rose bengal dye using Mn and Co doped TiO2 nanoparticles

Abstract

Mn/Co co-doped TiO₂ nanocomposite (Ti_0.89Mn_0.05Co_0.06O₂) was synthesized via a facile sol–gel route to enhance the visible-light photocatalytic degradation of Rose Bengal (RB) dye, a persistent organic pollutant in textile wastewater. The result of the incorporation of Mn and Co in the lattice of TiO₂ was confirmed by structural and morphological characterization techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared (FT-IR) spectroscopy. It is hypothesized that co-doping is more superior than single-metal doping due to the complementary electronic modification, in which Co induced lattice distortion and defect states reduces the band gap, and Mn introduces intermediate energy levels within the band gap which together play a role in effectively suppressing electron–hole recombination. In line with the proposed hypothesis, the optical band gap was found to decrease from 3.43 eV (pristine TiO₂) to 3.40 eV (TiO₂/Mn/Co) as determined by the UV–Vis Spectroscopy. The photoluminescence (PL) measurements revealed significant PL quenching, suggesting efficient charge-carrier separation. The TiO₂/Mn/Co nanocomposite degraded 94% of RB after 150 min under natural sunlight, whereas pristine TiO₂ degraded to 92% of the dye after 150 min, and it was identified that the reactive oxygen species (ROS) are the main species that degrade the dye molecule. The degradation kinetics were well fitted into pseudo-first-order model. The absolute gain on the degradation efficiency is small but is supported by a strong body of convergent structural, vibrational, and optoelectronic evidence of dual-metal incorporation, which together validate the suppression-of-recombination mechanism. Based on these results, Mn/Co co-doped TiO₂ can be considered a potential low-cost and scalable photocatalyst, which could be a valuable contribution to sustainable environmental technologies for the removal of dyes from contaminated wastewater through solar treatment.